Copolymer with high chemical homogeneity and use thereof for improving the cold flow properties of fuel oils

ABSTRACT

A copolymer with high chemical homogeneity, consisting of (A) 50 to 30% by weight of ethylene, (B) 50 to 70% by weight of C 4 - to C 24 -hydrocarbyl ester of (meth)acrylic acid, (C) 0 to 5% by weight of (meth)acrylic acid and (D) 0 to 10% by weight of copolymerizable monomers, obtainable by polymerizing a mixture of 80 to 60% by weight of ethylene, 20 to 40% by weight of (meth)acrylic acid and 0 to 10% by weight of copolymerizable monomers in a backmixing, continuous polymerization apparatus, and subsequently polymer-analogously esterifying the resulting copolymer with C 4 - to C 24 -hydrocarbinols. The inventive copolymer is suitable for improving the cold flow properties of fuel oils, for lowering the lower mixing temperature of cold flow improver additives into fuel oils, and for improving the filterability of fuel oils comprising cold flow improver additives.

The present invention relates to a copolymer with high chemicalhomogeneity, consisting of

-   (A) 50 to 30% by weight of ethylene,-   (B) 50 to 70% by weight of a C₄- to C₂₄-hydrocarbyl ester of acrylic    acid or methacrylic acid, or of a mixture of such hydrocarbyl    esters,-   (C) 0 to 5% by weight of acrylic acid and/or methacrylic acid and-   (D) 0 to 10% by weight of one or more copolymerizable monomers,

where all monomer components in the copolymer together add up to 100% byweight,

obtainable by polymerizing a mixture of 80 to 60% by weight of ethylene,20 to 40% by weight of acrylic acid and/or methacrylic acid and 0 to 10%by weight of one or more copolymerizable monomers, where all monomercomponents in the mixture together add up to 100% by weight, in abackmixing, continuous polymerization apparatus, and subsequentlypolymer-analogously esterifying the resulting copolymer of ethylene and(meth)acrylic acid or of essentially ethylene and (meth)acrylic acidwith a C₄- to C₂₄-hydrocarbinol or a mixture of C₄- toC₂₄-hydrocarbinols.

The present invention further relates to a process for preparing thiscopolymer with high chemical homogeneity.

The present invention further relates to the use of this terpolymer forimproving the cold flow properties of fuel oils, for lowering the lowermixing temperature of cold flow improver additives into fuel oils andfor improving the filterability of fuel oils comprising cold flowimprover additives.

Middle distillate fuels of fossil origin, especially gas oils, dieseloils or light heating oils, which are obtained from mineral oil, havedifferent contents of paraffins depending on the origin of the crudeoil. At low temperatures, there is precipitation of solid paraffins atthe cloud point (“CP”). In the course of further cooling, theplatelet-shaped n-paraffin crystals form a kind of “house of cardsstructure” and the middle distillate fuel ceases to flow even though itspredominant portion is still liquid. The precipitated n-paraffins in thetemperature range between cloud point and pour point (“PP”) considerablyimpair the flowability of the middle distillate fuels; the paraffinsblock filters and cause irregular or completely interrupted fuel supplyto the combustion units. Similar disruptions occur in the case of lightheating oils.

It has long been known that suitable additives can modify the crystalgrowth of the n-paraffins in middle distillate fuels. Very effectiveadditives prevent middle distillate fuels from solidifying even attemperatures a few degrees celsius below the temperature at which thefirst paraffin crystals crystallize out. Instead, fine, readilycrystallizing, separate paraffin crystals are formed, which, even whenthe temperature is lowered further, pass through filters in motorvehicles and heating systems, or at least form a filtercake which ispermeable to the liquid portion of the middle distillates, so thatdisruption-free operation is ensured. The efficacy of the flow improversis typically expressed, in accordance with European standard EN 116,indirectly by measuring the cold filter plugging point (“CFPP”).Ethylene-vinyl carboxylate copolymers such as ethylene-vinyl acetatecopolymers (“EVA”), for example, have already been used for some time ascold flow improvers or middle distillate flow improvers (“MDFIs”) ofthis kind.

The problems with the cold flow performance are similar for biofuel oils(“biodiesel”) and mixtures of middle distillate fuels and biofuel oils.It is possible here in principle to improve the cold flow performanceusing the same additives as in the case of pure middle distillate fuels.

One disadvantage of these additives when used in middle distillate fuelsis that the paraffin crystals modified in this way, owing to theirhigher density compared to the liquid portion, tend to settle out moreand more at the bottom of the vessel in the course of storage of themiddle distillate fuel. As a result, a homogeneous low-paraffin phaseforms in the upper part of the vessel, and a biphasic paraffin-richlayer at the bottom. Since the fuel is usually drawn off just above thevessel bottom both in vehicle fuel tanks and storage or supply tanks ofmineral oil dealers, there is the risk that the high concentration ofsolid paraffins leads to blockages of filters and metering devices. Thefurther the storage temperature is below the precipitation temperatureof the paraffins, the greater this risk becomes, since the amount ofparaffin precipitated increases with falling temperature. In particular,fractions of biodiesel also enhance this undesired tendency of themiddle distillate fuel to paraffin sedimentation. By virtue of theadditional use of paraffin dispersants or wax antisettling additives(“WASAs”), the problems outlined can be reduced.

WO 2008/059055 discloses terpolymers formed from ethylene, vinyl acetateand relatively long-chain (meth)acrylic esters, for example2-propylheptyl acrylate, as cold flow improvers for fuel oils.

In addition to the abovementioned ethylene-vinyl carboxylate copolymers,the prior art also recommends ethylene-(meth)acrylic ester copolymers ascold flow improvers for middle distillate fuels and biofuel oils. Forexample, DE 10 2006 022 720 A1 describes copolymers formed from 18 to 35mol % of one or more vinyl esters and/or (meth)acrylic esters and 65 to82% by weight of ethylene as an additive for improving the cold flowproperties of fuel oils of animal or vegetable origin. Acrylic ormethacrylic ester components emphasized are the C₁- to C₂₀-alkyl estersof acrylic acid and methacrylic acid, such as methyl (meth)acrylate,ethyl (meth)acrylate, propyl (meth)acrylate, n- and isobutyl(meth)acrylate, hexyl, octyl, 2-ethylhexyl, decyl, dodecyl, tetradecyl,hexadecyl and octadecyl (meth)acrylate.

It was an object of the present invention to provide products with highchemical homogeneity, which bring about very good cold performance infuel oils as a result of the high chemical homogeneity thereof. Moreparticularly, the PP value for these fuel oils should be loweredeffectively. At the same time, these products, owing to their highchemical homogeneity, should also lower the lower mixing temperature ofcold flow improver additives into fuel oils and improve thefilterability of fuel oils comprising cold flow improver additives.

The object is achieved in accordance with the invention by the copolymerhaving high chemical homogeneity cited at the outset, formed fromcomponents (A), (B), (C) and (D).

To characterize the “high chemical homogeneity” of the inventivecopolymer, the constancy of the values from the acid numberdeterminations for different copolymer fractions with different polymerchain lengths, which are obtained by fractional precipitation in thecourse of cooling of a solution of the inventive copolymer, should beemployed here. The definition of an inventive copolymer with “highchemical homogeneity” shall typically include, in the context of thepresent invention, all those copolymers which, in the course of coolingof a 20% by weight solution of the copolymer formed from components (A),(B), (C) and (D) in the composition specified, prepared by heating to60° C., in a mixture composed of the solvents decane and ethylbenzene ina weight ratio of 1:1, to +10° C., 0° C. and −10° C. in each case, giverise to precipitates which—together with the residue, freed of thesolvents, from the mother liquor of the last precipitation—afterfiltration and removal of the solvents, result in a total of 4fractions, the particular individual acid numbers of which are allwithin the value range of ±15%, especially ±10%, in particular ±5%, ofthe arithmetic mean of all 4 acid numbers determined. The acid numbersare determined here titrimetrically as usual in mg KOH/g of copolymer.

Suitable and preferred C₄- to C₂₄-hydrocarbinols are especially C₄- toC₂₄-alkanols, especially C₈- to C₁₈-alkanols, in particular C₁₀- toC₁₅-alkanols, and also C₇- to C₂₄-arylalkanols and C₅- toC₈-cycloalkanols.

The inventive copolymer is preferably formed from

-   (A) 45 to 35% by weight, especially 42 to 38% by weight, of    ethylene,-   (B) 55 to 65% by weight, especially 58 to 62% by weight, of a C₄- to    C₂₄-hydrocarbyl ester of acrylic acid or methacrylic acid, or of a    mixture of such hydrocarbyl esters,-   (C) 0 to 3.5% by weight, especially 0 to 2% by weight; of acrylic    acid and/or methacrylic acid and-   (D) 0 to 5% by weight, especially 0 to 2.5% by weight, of one or    more copolymerizable monomers.

Suitable C₄- to C₂₄-hydrocarbyl esters of acrylic acid or methacrylicacid for component (B) are preferably the alkyl esters of acrylic acidor methacrylic acid, especially the esters of acrylic acid andmethacrylic acid with C₈- to C₁₈-alkanols, especially C₁₀- toC₁₅-alkanols, for example with n-butanol, sec-butanol, isobutanol,tert-butanol, n-pentanol, tert-pentanol, n-hexanol, n-heptanol,n-octanol, 2-ethylhexanol, n-nonanol, isononanol, n-decanol,2-propylheptanol, n-undecanol, n-dodecanol, n-tridecanol, isotridecanol,n-tetradecanol, n-pentadecanol, n-hexadecanol, n-heptadecanol,n-octadecanol and n-eicosanol, and also the esters of acrylic acid andmethacrylic acid with C₇- to C₂₄-arylalkanols and with C₅- toC₈-cycloalkanols, for example with 1- or 2-phenoxyethanol, cyclopentanoland cyclohexanol. A minimum chain length of 4, especially of 8, inparticular of 10, carbon atoms in the case of alkanols is necessary forthe solubility performance of the inventive copolymer in the fuel oils.

The inventive copolymer may also comprise, in copolymerized form, two ormore species of the C₄- to C₂₄-hydrocarbyl esters of acrylic acid ormethacrylic acid mentioned as component (B).

In a preferred embodiment, the inventive copolymer comprises, ascomponent (B), a C₈- to C₁₈-alkyl ester of acrylic acid or methacrylicacid or of a mixture of such alkyl esters.

The inventive copolymer is obtainable by polymerizing a mixture of 80 to60% by weight of ethylene, 20 to 40% by weight of acrylic acid and/ormethacrylic acid and 0 to 10% by weight of one or more copolymerizablemonomers, where all monomer components in the mixture together add up to100% by weight, in a backmixing, continuous polymerization apparatus,and subsequently polymer-analogously esterifying the resulting copolymerof ethylene and (meth)acrylic acid or of essentially ethylene and(meth)acrylic acid with a C₄- to C₂₄-hydrocarbinol or a mixture of C₄-to C₂₄-hydrocarbinols. The polymerization step is normally performed bythe customary high-pressure polymerization techniques at a pressure of50 to 5000 bar, especially 1000 to 2500 bar, in particular 500 to 2000bar, typically 1600 to 1800 bar. In general, the temperatures employedare 50 to 450° C., especially 100 to 350° C., in particular 150 to 250°C., typically 200 to 240° C. The polymerization apparatus used ispreferably a backmixing, continuous autoclave. In general, thepolymerization is initiated by means of free-radically decomposinginitiators, for which air or oxygen are suitable, optionally in thepresence of additionally metered organic peroxides and/orhydroperoxides.

Useful organic peroxides or hydroperoxides include, for example,diisopropylbenzene hydroperoxide, cumene hydroperoxide, methyl isobutylketone peroxide, di-tert-butyl peroxide and tert-butyl periisononate. Inaddition, suitable regulators such as aliphatic aldehydes may also beused in the polymerization.

The desired relatively low proportion by weight of ethylene in theinventive copolymer arises from the fact that, proceeding from a readilypolymerizable monomer mixture in which the ethylene content predominatesover the (meth)acrylic acid content, and the proportion by weight of theunit derived from (meth)acrylic acid in the polymer, is increasedsignificantly by subsequent polymer-analogous esterification of thecarboxyl groups in the polymer with one or more C₄- toC₂₄-hydrocarbinols. This route is also favorable because directpolymerization of ethylene with C₄- to C₂₄-hydrocarbyl esters of acrylicacid or methacrylic acid is controllable only with difficulty. Only bythis route are copolymers of ethylene and (meth)acrylic acid or ofessentially ethylene and (meth)acrylic acid with the desired highchemical homogeneity obtained. Since the esterification of the secondreaction stage may not proceed to completion, the inventive copolymermay comprise up to 5% by weight of unesterified (meth)acrylic acidunits.

Suitable monomers (D) used in addition if desired are especially organicmolecules with one or more polymerizable vinyl groups, for example vinylacetate, vinyl propionate, vinyl butanoate, vinyl pentanoate, vinylhexanoate, vinyl 2-ethylhexanoate, vinyl octanoate, vinyl esters ofneodecanoic acid (“Veova”), vinyl decanoate, vinyl dodecanoate, vinyltridecanoate, vinyl isotridecanoate, vinyl tetradecanoate, vinylpentadecanoate, vinyl hexadecanoate and vinyl octadecanoate, andadditionally also vinylphosphoric esters such as dimethyl vinylphosphateor diethyl vinylphosphate, or vinylsilane (H₂C═CH—SiH₃). Also suitablehere are vinyl ethers such as cyclohexyl vinyl ether, isopropyl vinylether, isobutyl vinyl ether, tert-butyl vinyl ether, n-butyl vinylether, octyl vinyl ether, decyl vinyl ether, dodecyl vinyl ether,tetradecyl vinyl ether, hexadecyl vinyl ether and octadecyl vinyl ether.

The polymer-analogous esterification step of the second reaction stageis performed by customary esterification techniques. Preference is givenhere to working with acidic esterification catalysts such asmethanesulfonic acid, para-toluenesulfonic acid, trifluoroacetic acid,sulfuric acid or hydrogen chloride. The water of reaction which forms isdriven out typically by passing through inert gas, such as nitrogen, atelevated temperatures, especially at 120 to 200° C.

The inventive copolymer preferably has a number-average molecular weight(M_(n)) in the range from 1000 to 10 000, especially from 1500 to 3500,or alternatively a weight-average molecular weight of 2000 to 20 000,especially of 3000 to 7000 (in each case determined by gel permeationchromatography).

The present invention also provides a process for preparing a copolymerwith high chemical homogeneity, consisting of

-   (A) 50 to 30% by weight of ethylene,-   (B) 50 to 70% by weight of a C₄- to C₂₄-hydrocarbyl ester of acrylic    acid or methacrylic acid, or of a mixture of such hydrocarbyl    esters,-   (C) 0 to 5% by weight of acrylic acid and/or methacrylic acid and-   (D) 0 to 10% by weight of one or more copolymerizable monomers,

where all monomer components in the copolymer together add up to 100% byweight,

which comprises polymerizing a mixture of 80 to 60% by weight ofethylene, 20 to 40% by weight of acrylic acid or methacrylic acid and 0to 10% by weight of one or more copolymerizable monomers, where allmonomer components in the mixture together add up to 100% by weight, ina backmixing, continuous polymerization apparatus, especially in abackmixing, continuous autoclave, preference being given to working at apressure of 50 to 5000 bar, and subsequently polymer-analogouslyesterifying the resulting copolymer of ethylene and (meth)acrylic acidor of essentially ethylene and (meth)acrylic acid with a C₄- toC₂₄-hydrocarbinol or a mixture of C₄- to C₂₄-hydrocarbinols.

The inventive copolymer serves as a novel efficient cold flow improverin fuel oils. Fuel oils shall be understood in the context of thepresent invention to mean middle distillate fuels of fossil, vegetableor animal origin, biofuel oils (“biodiesel”) and mixtures as such middledistillate fuels and biofuel oils.

Middle distillate fuels (also referred to hereinafter as “middledistillates” for short) refer in particular to fuels which are obtainedby distilling crude oil as the first process step and boil within therange from 120 to 450° C. Such middle distillate fuels are usedespecially as diesel fuel, heating oil or kerosene, particularpreference being given to diesel fuel and heating oil. Preference isgiven to using low-sulfur middle distillates, i.e. those which compriseless than 350 ppm of sulfur, especially less than 200 ppm of sulfur, inparticular less than 50 ppm of sulfur. In special cases, they compriseless than 10 ppm of sulfur; these middle distillates are also referredto as “sulfur-free”. They are generally crude oil distillates which havebeen subjected to refining under hydrogenating conditions and thereforecomprise only small proportions of polyaromatic and polar compounds.They are preferably those middle distillates which have 90% distillationpoints below 370° C., in particular below 360° C. and in special casesbelow 330° C.

Low-sulfur and sulfur-free middle distillates may also be obtained fromrelatively heavy mineral oil fractions which cannot be distilled underatmospheric pressure. Typical conversion processes for preparing middledistillates from heavy mineral oil fractions include: hydrocracking,thermal cracking, catalytic cracking, coking processes and/orvisbreaking. Depending on the process, these middle distillates areobtained in low-sulfur or sulfur-free form, or are subjected to refiningunder hydrogenating conditions.

The middle distillates preferably have aromatics contents of below 28%by weight, especially below 20% by weight. The content of normalparaffins is between 5% by weight and 50% by weight, preferably between10 and 35% by weight.

In the context of the present invention, middle distillate fuels shallalso be understood here to mean fuels which can either be derivedindirectly from fossil sources such as mineral oil or natural gas, orelse are prepared from biomass via gasification and subsequenthydrogenation. A typical example of a middle distillate fuel which isderived indirectly from fossil sources is the GTL (“gas-to-liquid”)diesel fuel obtained by means of Fischer-Tropsch synthesis. A middledistillate is prepared from biomass, for example via the BTL(“biomass-to-liquid”) process, and can be used either alone or in amixture with other middle distillates as the fuel. The middledistillates also include hydrocarbons which are obtained by thehydrogenation of fats and fatty oils. They comprise predominantlyn-paraffins.

The qualities of the heating oils and diesel fuels are laid down in moredetail, for example, in DIN 51603 and EN 590 (cf. also Ullmann'sEncyclopedia of Industrial Chemistry, 5th edition, volume A12, p. 617ff.).

The inventive copolymer can, in addition to the use thereof in themiddle distillate fuels, of fossil, vegetable or animal originmentioned, which are essentially hydrocarbon mixtures, also be used inbiofuel oils and in mixtures of the middle distillates mentioned withbiofuel oils to improve the cold flow performance. Such mixtures arecommercially available and usually contain the biofuel oils in minoramounts, typically in amounts of 1 to 30% by weight, especially of 3 to10% by weight, based on the total amount of middle distillate of fossil,vegetable or animal origin and biofuel oil.

Biofuel oils are generally based on fatty acid esters, preferablyessentially on alkyl esters of fatty acids which derive from vegetableand/or animal oils and/or fats. Alkyl esters are typically understood tomean lower alkyl esters, especially C₁- to C₄-alkyl esters, which areobtainable by transesterifying the glycerides which occur in vegetableand/or animal oils and/or fats, especially triglycerides, by means oflower alcohols, for example ethanol or in particular methanol (“FAME”).Typical lower alkyl esters based on vegetable and/or animal oils and/orfats, which find use as a biofuel oil or components therefor, are, forexample, sunflower methyl ester, palm oil methyl ester (“PME”), soya oilmethy ester (“SME”) and especially rapeseed oil methyl ester (“RME”).

The inventive copolymer brings about a significant improvement in thecold flow performance of the fuel oil, i.e. a lowering especially of thePP values, but also of the CP values and/or of the CFPP values,substantially irrespective of the origin or of the composition of thefuel oil. Precipitated paraffin crystals and crystals of fatty acidesters are generally kept suspended more effectively, such that thereare no blockages of filters and lines by such sediments. In most cases,the inventive copolymer has a good range of action and thus has theeffect that the precipitated crystals can be dispersed very efficientlyin a wide variety of different fuel oils.

The inventive copolymer additionally brings about a lowering of thelower mixing temperature of cold flow improver additives into fuel oils.Owing to the chemical structure thereof, cold flow improver additivesfrequently have to be added to the refinery streams at a particularelevated minimum temperature in order to enable pumped addition andcomplete dissolution in the fuel oil and the homogenization thereof.This parameter—also defined as the lower mixing temperature—should be ata minimum in order to avoid costly heating of the cold flow improverstorage tanks in the refineries.

The inventive copolymer additionally brings about an improvement in thefilterability of fuel oils comprising cold flow improver additives. Thisis because the presence of prior art additives leads in many cases to adeterioration in the filterability of fuel oils, which restricts theusability and the maximum dosage of the additives.

The use of the inventive copolymer may likewise, in addition to theimprovement in the cold flow properties of fuel oils and of the handlingwith cold flow improver additives or with fuel oils comprising cold flowimprover additives, improve a series of further fuel of properties. Byway of example, mention shall be made here merely of the additionaleffect as an anticorrosive or the improvement in the oxidationstability.

The present invention also provides fuel oils which comprise 10 to 5000ppm by weight especially 25 to 1500 ppm by weight, in particular 50 to750 ppm by weight, of the inventive copolymer.

The fuel oils mentioned may comprise, as further additives, in amountscustomary therefor, further cold flow improvers, paraffin dispersants,conductivity improvers, anticorrosive additives, lubricity additives,antioxidants, metal deactivators, antifoams, demulsifiers, detergents,cetane number improvers, solvents or diluents, dyes or fragrances ormixtures thereof. Further cold flow improvers are described, forexample, in WO 2008/113757 A1. The other further additives mentionedabove are, incidentally, familiar to the person skilled in the art andtherefore need not be explained any further here.

The examples which follow are intended to illustrate the presentinvention without restricting it.

EXAMPLES Fuels Used

To demonstrate the effectiveness of the inventive copolymer as anadditive in biofuel oils, two typical commercial biodiesel qualities(test oils B1, B2 and B3) with the following properties were used:

B1: Type: RME Origin: Perstorp Sweden CP (DIN EN 23015): −4.0° C. CFPP(DIN EN 116) −11° C. PP (ASTM D 97) −12° C. Density at 15° C. (EN ISO1285): 882.8 kg/m³ B2: Type: FAME Origin: Rossi Biofuel CP (DIN EN23015): −3.8° C. CFPP (DIN EN 116) −9° C. PP (ASTM D 97) −6° C. Densityat 15° C. (EN ISO 1285): 883.0 kg/m³ B3: Type: RME Origin: commercialSwedish biodiesel CP (DIN EN 23015): −5.0° C. CFPP (DIN EN 116) −11° C.PP (ASTM D 97) −12° C. Density at 15° C. (EN ISO 1285): 883.1 kg/m³

Additives Used:

The ter- or copolymers used can be characterized as follows, T-1(according to WO 2008/059055, commercial product) having been used forcomparison and T-2 in accordance with the invention:

T-1: Composition: 60.0% by weight of ethylene 22.5% by weight of vinylacetate 17.5% by weight of 2-propyiheptyl acrylate Molecular Mn = 3000g/mol, Mw = 7300 g/mol weights: Viscosity: 170 mPas at 120° C. T-2:Composition: 40.1% by weight of ethylene 58.7% by weight of tridecylmethacrylate 1.2% by weight of methacrylic acid Molecular Mn = 3000g/mol, Mw = 7000 g/mol weights: Viscosity: <30 mPas at 120° C. preparedby high-pressure polymerization of a monomer mixture of 70.0% by weightof ethylene and 30.0% by weight of methacrylic acid at 220° C.and 1707bar and subsequent esterification with excess tridecanol (molar ratio ofmethacrylic acid units to tridecanol: 1:1.2) in the presence ofmethanesulfonic acid

Example 1 Determination of the Cold Performance

Table 1 below, containing the pour points (“PP”) determined by means ofa standardized test method, shows that the effect of the inventiveterpolymer (T-2) is significantly better than that of comparable priorart polymers (T-1).

TABLE 1 Determination of the PP values [°C.] Test oil Dosage* B1 B2 B3900 ppm 900 ppm 500 ppm Additive T-1 −15 −18 −12 Additive T-2 −38 −36−39 *Polymers T-1 and T-2 were each metered in as a concentratedsolution in a customary solvent. The dosage specified in each case isbased on the polymer content of the solution.

1. A copolymer with high chemical homogeneity, consisting of (A) 50 to30% by weight of ethylene, (B) 50 to 70% by weight of a C₄- toC₂₄-hydrocarbyl ester of acrylic acid or methacrylic acid, or of amixture of such hydrocarbyl esters, (C) 0 to 5% by weight of acrylicacid and/or methacrylic acid and (D) 0 to 10% by weight of one or morecopolymerizable monomers, where all monomer components in the copolymertogether add up to 100% by weight, obtainable by polymerizing a mixtureof 80 to 60% by weight of ethylene, 20 to 40% by weight of acrylic acidand/or methacrylic acid and 0 to 10% by weight of one or morecopolymerizable monomers, where all monomer components in the mixturetogether add up to 100% by weight, in a backmixing, continuouspolymerization apparatus, and subsequently polymer-analogouslyesterifying the resulting copolymer of ethylene and (meth)acrylic acidor of essentially ethylene and (meth)acrylic acid with a C₄- toC₂₄-hydrocarbinol or a mixture of C₄- to C₂₄-hydrocarbinols.
 2. Acopolymer with high chemical homogeneity according to claim 1,obtainable by polymerizing at a pressure of 50 to 5000 bar.
 3. Acopolymer with high chemical homogeneity according to claim 1,consisting of (A) 45 to 35% by weight, especially 42 to 38% by weight,of ethylene, (B) 55 to 65% by weight, especially 58 to 62% by weight, ofa C₄- to C₂₄-hydrocarbyl ester of acrylic acid or methacrylic acid, orof a mixture of such hydrocarbyl esters, (C) 0 to 3.5% by weight,especially 0 to 2% by weight; of acrylic acid and/or methacrylic acidand (D) 0 to 5% by weight, especially 0 to 2.5% by weight, of one ormore copolymerizable monomers.
 4. A copolymer with high chemicalhomogeneity according to claim 1, which comprises, as component (B), aC₈- to C₁₈-alkyl ester of acrylic acid or methacrylic acid or of amixture of such alkyl esters.
 5. A copolymer according to claim 1,having a number-average molecular weight in the range from 1000 to 10000, especially from 1500 to 3500, or having a weight-average molecularweight of 2000 to 20 000, especially of 3000 to
 7000. 6. A process forpreparing a copolymer with high chemical homogeneity, consisting of (A)50 to 30% by weight of ethylene, (B) 50 to 70% by weight of a C₄- toC₂₄-hydrocarbyl ester of acrylic acid or methacrylic acid, or of amixture of such hydrocarbyl esters, (C) 0 to 5% by weight of acrylicacid and/or methacrylic acid and (D) 0 to 10% by weight of one or morecopolymerizable monomers, where all monomer components in the copolymertogether add up to 100% by weight, which comprises polymerizing amixture of 80 to 60% by weight of ethylene, 20 to 40% by weight ofacrylic acid and/or methacrylic acid and 0 to 10% by weight of one ormore copolymerizable monomers, where all monomer components in themixture together add up to 100% by weight, in a backmixing, continuouspolymerization apparatus, and subsequently polymer-analogouslyesterifying the resulting copolymer of ethylene and (meth)acrylic acidor of essentially ethylene and (meth)acrylic acid with a C₄- toC₂₄-hydrocarbinol or a mixture of C₄- to C₂₄-hydrocarbinols.
 7. Theprocess according to claim 6, wherein polymerization is effected at apressure of 50 to 5000 bar.
 8. The process according to claim 6, whereinthe mixture of 80 to 60% by weight of ethylene, 20 to 40% by weight ofacrylic acid and/or methacrylic acid and 0 to 10% by weight of one ormore copolymerizable monomers is polymerized in a backmixing, continuousautoclave. 9-12. (canceled)